The present invention relates to chairs of the type which are used in offices, such as for secretarial or managerial use wherein a person occupies the chair for extended periods of time and the chair should be designed to provide not only sustained comfort to the occupant but to facilitate the performance of a large variety of tasks and a large number of positions and movements. More specifically, the present invention relates to an office chair in which the seat of the chair is vertically adjustable by means of a pneumatic cylinder and the backrest is independently adjustable for postural attitude. The postural attitude adjustment is also achieved with a pneumatic cylinder. Both cylinders are actuated by the same cam which is mounted to a shaft which extends laterally outwardly beneath the seat and includes a handle to facilitate rotation of the cam shaft by the occupant to the various operating positions.
When the cam shaft is rotated in one direction, a first surface of the cam unlocks a vertically oriented pneumatic cylinder forming a pedestal of the chair so that the seat may be adjusted in height. The vertical pneumatic cylinder is biased in such a way as to offset the weight of the seat, frame and backrest such that when the chair is unoccupied, these elements will rise as a unit. Height adjustment is accomplished by the occupant's using his or her weight to overcome the upward bias on the vertical cylinder. When the seat is in the desired adjusted position, the cam is rotated to the neutral position to lock the vertical cylinder.
The backrest assembly includes a support channel which is pivotally mounted to the rear of the base of the seat near the sacral region of the occupant. The lower end of the back support member is pivotally connected to the back adjusting pneumatic cylinder, and the backrest assembly is mounted to the upper end of the back support member. By rotating the cam shaft in a direction opposite to that which unlocked the height-adjusting vertical pneumatic cylinder, a second cam surface unlocks the back adjusting cylinder to permit the occupant to adjust the backrest in postural attitude about the pivotal connection of the back support member to the rear of the seat base.
This second cam surface which unlocks the backrest adjusting cylinder also includes a detent which may be stably positioned on the valve actuator of the adjusting cylinder for the backrest for continuously actuating or unlocking the backrest cylinder to provide a floating support or dynamic cushioning to the back of the occupant.
The backrest cushion assembly is mounted to its support by means of a pair of laterally spaced cushion mounts which provide lesser resistance to body motion in a fore-and-aft direction and greater support to reaching motions of the occupant in a lateral or rearward direction where such support is desired.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals refer to like parts in the various views.